Cocaine- and amphetamine-regulated transcript peptide produces anxiety-like behavior in rodents

Abstract

Cocaine- and amphetamine-regulated transcript (CART) peptide (CART-(55–102)) is involved in the suppression of food intake. We now report that CART-(55–102) is involved in anxiety in rodents. Intracerebroventricularly administered CART-(55–102) as well as intraperitoneal administration of N-methyl-β-carboline-3-carboxamide (FG-7142), a selective GABA_A/benzodiazepine receptor inverse agonist, reduced time spent in the open arms in the elevated plus-maze task in mice. CART-(55–102)-induced anxiogenic-like behavior in this task was attenuated by widely prescribed anxiolytics such as diazepam and buspirone. Likewise, CART-(55–102) and FG-7142 significantly reduced social interaction in mice. Both diazepam and buspirone significantly reversed CART-(55–102)-induced anxiogenic-like behavior in social interaction tests. By contrast, another biologically active CART peptide, CART-(62–102), was without effect in the elevated plus-maze task in mice. Moreover, intracerebroventricular administration of CART-(55–102) markedly increased the firing rate of locus coeruleus neurons in single unit recording in anesthetized rats. As CART-(55–102) produced anxiety-like effects in rodents, this peptide may possibly be involved in anxiety and stress-related behavior.

Introduction

Cocaine- and amphetamine-regulated transcript (CART) was originally described to be an mRNA acutely upregulated in the nucleus accumbens after administration of cocaine or amphetamine in rats (Douglass et al., 1995). To date, several CART peptide fragments have been identified Kuhar and Yoho, 1999, Thim et al., 1999. Among them, two CART peptide fragments, CART-(55–102) and CART-(62–102), were isolated and sequenced from the rat hypothalamus and pituitary Kristensen et al., 1998, Thim et al., 1998, Thim et al., 1999, and found to be biologically active Kristensen et al., 1998, Bannon et al., 2001. There are several lines of evidence that CART-(55–102) is deeply involved in feeding behavior and energy expenditure Kristensen et al., 1998, Thim et al., 1998, Wang et al., 2000. Intracerebroventricular administration of CART-(55-102) suppresses food intake in normal and fasted rats Kristensen et al., 1998, Thim et al., 1998, and induces c-Fos in the brain in the areas related to feeding and energy balance Vrang et al., 1999, Vrang et al., 2000. CART mRNA is also expressed abundantly within hypothalamic structures implicated in the central control of feeding behavior and metabolism, and leptin administration increases CART mRNA in the hypothalamus (Kristensen et al., 1998). In addition to CART-(55–102), CART-(62–105) was also reported to cause a marked reduction in food intake in fasted mice (Bannon et al., 2001).

In addition to abundant expression in the hypothalamus, CART mRNA and CART peptide immunoreactivity are expressed in other brain areas, including the pituitary and limbic systems such as central and basomedial nucleus of amygdala, and septum-hippocampal formation Couceyro et al., 1997, Koylu et al., 1997, Koylu et al., 1998. CART-(55–102) administration induces c-Fos expression in the central nucleus of amygdala as well as in the paraventricular nucleus of the hypothalamus Vrang et al., 1999, Vrang et al., 2000. Moreover, in paraventricular nucleus, 89% of cortocotropin-releasing hormone (CRH)-immunoreactive neurons contain c-Fos after i.c.v. injection of CART-(55–102), and CART-(55–102) markedly induces plasma adrenocorticotropic hormone (ACTH) and corticosterone levels Stanley et al., 2001, Vrang et al., 2000. CART-(55–102) also increases release of CRH from hypothalamic explants (Stanley et al., 2001). These findings indicate that CART-(55–102) may activate the hypothalamus–pituitary–adrenal axis, possibly by interacting with the CRH system, and that CART peptides may be involved in emotional regulation and stress responses. Both CART-(55–102) and CART-(62–102) have been reported to have multiple physiological roles in the central nervous system other than the regulation of food intake Bannon et al., 2001, Kimmel et al., 2000, Matsumura et al., 2001, Okumura et al., 2000, and another fragment of CART peptides was reported to induce anxiogenic-like activity in rats (Kask et al., 2000). In the present study, we investigated the involvement of CART-(55–102) and CART-(62–102) in anxiety in rodents.